While not limited thereto the present invention is particularly adapted for use in the production of metal alloys, such as steel, of various compositions. In the production of steel, for example, it is known to employ tuyeres to inject gas into the molten metal for the purpose of deoxidation, decarburization, desulfurization and stirring. Usually, the tuyeres extend through a refractory lining of a basic oxygen furnace, ladle or tundish; and in some cases a plurality of tuyeres are used in order to insure the proper amount of gas injection into the molten metal to carry out the desired process of decarburization, desulfurization, etc. In the case of a BOF vessel, for example, tuyeres are usually located adjacent the bottom portion of the vessel.
While it is heretofore been known to introduce a gas or mixture of gasses into a metal bath with the use of tuyeres or porous plugs, such prior art tuyeres introduce the gas into the metal bath in a straight line path rather than at an angular or circulatory path.
It is known in accordance with the prior art to introduce oxygen gas from a spiral type lance under the surface of a molten steel bath as described, for example, in U.S. Pat. No. 3,645,520. A consumable type lance of the type described in the aforesaid patent, however, is used primarily for the decarburization of molten metal and, as mentioned above, is blown under the surface of the molten metal bath rather than through the refractory side walls of a vessel.
A consumable type spiral lance for blowing oxygen under the surface of a molten steel bath is also expensive and must be replaced after every one or two heats. As will be seen, the tuyeres of the present invention are designed to last the life of the vessel, which is normally 400 or more heats before a rebuild is required.
While a spiral-type lance has been suggested in the past for blowing oxygen under the surface of a molten steel bath, problems associated with spiral injection below the level of the molten bath through tuyeres are entirely different. To begin with, when a gas is injected from a lance above a molten metal bath, there is no danger of refractory erosion in the area immediately surrounding the lance also, the lance is consumed as it erodes in the molten metal bath and must be fed downwardly to keep the gas flow under the surface of the bath. When gas is injected from a tuyere, however, care must be taken such that a strong metal flow is not set up against the surrounding refractory. Such a flow contributes to a premature failure of the refractory. Furthermore, tuyere pressures must be closely regulated in order to avoid a buildup at the end of the tuyere known to those skilled in the art as "mushrooms" or "knurdles". Similarly, a burn back at the face of the tuyere could result in premature failure of the tuyere and/or vessel. These considerations are the subject of a mathematical model for a straight pipe tuyere described in U.S. Pat. No. 4,462,824.